The following background information is provided to assist the reader to understand the invention described and claimed below. Accordingly, any terms used herein are not intended to be limited to any particular narrow interpretation unless specifically stated otherwise in this document.
A railway operating authority is responsible for conducting rail traffic safely along the railway track routes under its control. A train is typically conducted safely along a railway route through the use of a wayside signaling system. One type of wayside signaling system shown in FIG. 1A features a continuous succession of DC train detection circuits along the entire length of the railway route through which to control a multiplicity of wayside signal devices spaced apart from each other along the route. Each train detection circuit covers a section of track approximately 10,000 feet in length and is electrically isolated from the next detection circuit via an insulated joint situated between each track section. Each train detection circuit merely detects whether its section of track is occupied by a train and communicates a signal indicative of same to its corresponding wayside signal device. For the wayside signaling system shown in FIG. 1A, each wayside signal device typically takes the form of a display of colored lights or other indicia through which to visually communicate signal aspect information to a train operator. It is the signal aspect information that denotes the condition of the upcoming segment of track, i.e., whether it is clear, occupied by a train or subject to some other speed restriction.
Each signal aspect is conveyed by a color or combination of colors and denotes a particular course of action required by the operating authority. The particular colors of red, yellow and green generally denote the same meaning as when used on a standard traffic light. In a four aspect wayside signaling system, for example, the following scheme may be employed: green for clear, yellow and green for approach medium, yellow for approach, and red for restricted/stop. If a train is detected on a section of track, the train detection circuit corresponding thereto informs its corresponding wayside signal device. As the train approaches a track segment over which the wayside signal device has coverage, the railway authority that operates that segment then uses the wayside signal device to communicate visually the appropriate signal aspect to the train operator.
Another type of wayside signaling system shown in FIG. 1B also features the continuous succession of DC train detection circuits along the railway track route. They, too, are used to control the wayside signal devices spaced along the route. Each of the wayside signal devices in this type of signaling system also includes an AC track circuit that accompanies or overlays each DC train detection circuit and serves to supplement its visual display. Each wayside signal device through its AC track circuit communicates over the rails the signal aspect information (i.e., the cab signal) up to a range of approximately 5,000 feet. As a train rides on the rails, the cab signal is sensed by pick up coils mounted in front of the leading axle of the locomotive. The cab signal is filtered, decoded and eventually conveyed to a cab signal device located in the cab of the locomotive. The cab signal device typically includes a display of colored lights to convey visually the signal aspect information to the train operator.
Most railway operating authorities such as Conrail and Union Pacific, for example, use a four aspect system to communicate the condition of the upcoming track segment. Each of the wayside signal devices in such a system typically takes the form of an AC power frequency track circuit from which a carrier frequency typically ranging between 50 to 100 Hertz carries the cab signal in coded format. In this four aspect wayside signaling system, each signal aspect is communicated via electrical pulses in the aforementioned way to the cab signal device using the following preset code rates: 180 pulses per minute for Clear, 120 for Approach Medium, 75 for Approach, and 0 for Restricted/Stop. The latter three aspects each impose a restriction in the speed with which the train may proceed along that segment of railway track.
Railway equipment manufacturers have offered a variety of systems whose objective is to operate the brakes of a train in compliance with such directions issued by the railway operating authorities. These systems typically employ the cab signal devices in conjunction with automatic train protection (ATP) systems. By processing the directions received from the wayside signaling systems according to known principles, such prior art devices and systems are used to derive, and require the train to comport with, braking profiles. These prior art systems typically brake the train automatically when the train operates contrary to the limits imposed by the braking profiles and thus contrary to the wayside signaling system on which the train is riding.
The cab signal device thus typically features an audible warning device and an acknowledgment input. The acknowledgment input allows the train operator to acknowledge the more restrictive signal aspects and thereby prevent a penalty brake application. For example, when the train encounters a segment of track over which one of the speed restrictions is in force and the train is nevertheless permitted to exceed the speed restriction, the cab signal device will activate the audible warning device. If the train operator does not initiate a service brake application so that the train comports with the calculated speed distance braking profile, the cab signal device will automatically impose a penalty brake application to stop the train. The cab signal device typically provides power continuously to a feed circuit to energize, and thus keep closed, an electropneumatic valve. Should the train run afoul of the speed distance braking profile, the cab signal device deenergizes the valve to vent the brake pipe to atmosphere thereby applying the brakes. In newer locomotives equipped with modern brake control systems such as the WABCO EPIC.RTM. systems, the cab signal device offers a similar input to the electronic brake control system to provide the same function.
Some cab signal devices also offer overspeed protection as an optional feature. A speed sensing device provides an indication of speed to the cab signal device. The cab signal device automatically shuts down the engine of the locomotive if the speed of the train exceeds a predetermined value.
The territorial coverage of the DC train detection circuits and the wayside signal device AC track circuits is typically not coextensive. Whereas each DC train detection circuit covers a section of track approximately 10,000 feet in length, each wayside signal device through its AC track circuit can typically apply its cab signal on a reliable basis to a range of about 5,000 feet. Consequently, repeater units are often used to fill the gaps so as to provide continuous cab signal coverage between wayside signal devices as shown in FIG. 1B.
The cab signal devices on present day trains are designed to operate on wayside signaling systems that provide continuous coverage over the entire track route. Should a wayside signal device or a repeater unit fail, the cab signal device will interpret the loss of signal aspect information as a stop aspect and automatically impose a penalty brake application. Though the train operator can typically prevent a penalty brake application by acknowledgment or other actions, it is generally not operationally acceptable to routinely require repeated wayside signal "cut-out" and "cut-in" procedures to cover such loss of coverage. Though such wayside signaling systems are widely used on both freight railroads and passenger transit properties, they have not been extensively deployed on the longer freight railroad routes. This is primarily due to cost considerations. It is quite expensive to equip railway track routes with wayside signal devices let alone the necessary repeater units. The need for repeater units alone can often more than double the cost of implementing a wayside signaling system. This increase in cost is due to the need for infrastructure such as acquiring sites at which to install the equipment and providing the foundations, equipment housings and power access at those sites. Many railway routes therefore have the type of wayside signaling system shown in FIG. 1C in which there are gaps in cab signal coverage because repeater units either are not used or only used in certain places.
For heavy freight trains with conventional continuous cab signal devices, it is generally not practical to provide automatic train stop techniques to enforce braking. Several factors such as the braking characteristics, the signal block lengths and grades for any given train and terrain are not known and thus worst case conditions would therefore have to be assumed. This would result in overly restrictive braking curve assumptions for most cases, which would affect train operations too severely to be practical. Consequently, most freight train operators with continuous cab signal devices (e.g., Conrail and Union Pacific Railroads), provide only a warning of the more restrictive signal aspects, with an acknowledgment requirement. The penalty brakes are applied automatically only if the train operator fails to acknowledge the more restrictive signal aspects. The train operator can thus satisfy the acknowledgment requirement, yet still not apply the brakes so as to stop the train before approaching a red signal.
Yet another type of wayside signaling system (not shown) also features the continuous succession of DC train detection circuits along the railway track route. They, too, are used to control the wayside signal devices spaced along the route. In this type of wayside signaling system, however, each of the wayside signal devices controls a track transponder located at a fixed point along the track before each wayside signal device. When a train is detected on a section of track, the train detection circuit corresponding thereto informs its corresponding wayside signal device. The train, however, can only receive the signal aspect information from the transponder as it passes by each fixed point. By using the track transponders to transmit additional encoded data such as the profile of the upcoming track segment and the signal block length, a train equipped with an automatic train protection (ATP) system is able to enforce braking on routes covered by such a wayside signaling system.
The primary disadvantage of transponder based ATP systems is that trains so equipped are required to pass discrete points on the railway track to receive the updated signal aspect information. Some railway authorities have therefore used radio systems to supplement the information received from the track transponders. Other authorities have used fixed transponders only, with updated information transmitted by radio from the wayside signal devices.
Another shortcoming common to all transponder based ATP systems is that they are rather expensive to install and maintain. Maintenance, for example, typically requires replacement of transponders that are damaged. Maintenance may also require a change in the codes or the locations of the transponders as the configuration of the railway track may well be changed over time.
Current automatic train protection systems present significant disadvantages whether used in connection with wayside signaling systems featuring wayside signal devices having AC track circuits or fixed point transponders. For wayside signaling systems featuring wayside signal devices that employ AC track circuits, it is expensive to equip railway routes with repeater units to prevent gaps in coverage from which signal aspect information would be unavailable. Moreover, the cab signal device will interpret such loss of the cab signal as a stop aspect and automatically impose a penalty brake application. For wayside signaling systems featuring wayside signal devices that employ fixed point transponders, a train equipped for travel on such routes is required to pass fixed points to receive the updated signal aspect and guidance information from the transponders. Transponder systems are also expensive to install and maintain.
There is therefore a need in the railroad industry for a system that could operate the brakes of a train in compliance with a wayside signaling system without the aforementioned disadvantages. Specifically, it would be quite desirable to develop a system not dependent on fixed point transponders to receive information from the wayside signaling system. Moreover, it would be preferred if such a system would not require the installation of expensive repeater units to fill gaps in cab signal coverage between wayside signal devices. Such a system should be able to operate the brakes in compliance with a wayside signaling system even if the system encounters track segments (i.e., gaps) from which signal aspect information/cab signal is unavailable. Such a system would ideally be designed to operate on either or both of the wayside signaling systems shown in FIGS. 1B and 1C.
Related to the invention is subject matter described and claimed in U.S. Pat. No. 5,740,547 entitled Rail Navigation System, This patent is assigned to the assignee of the present invention, and its teachings are incorporated into the present document by reference. The rail navigation system allows a train to locate the position it occupies on a railway track route.
As best described in the cited document, the rail navigation system features a database including data pertaining to the locations of railway track routes and the locations and orientations of curves and switches in those railway track routes. It also receives inputs from devices such as an odometer, a rate of turn measuring apparatus and a navigational receiver. According to instructions contained within its programming code, the rail navigation system uses the aforementioned data along with and in comparison to the enumerated inputs to determine where the train is located in relation to track route location data stored in the on-board database. Through such processing, the coordinates the train occupies on the globe is matched against the database information to determine not only on which track the train is traveling but also the particular position that the train occupies on that track.